Many different types of manufacturing operations rely on large quantities of water for various reasons, such as for cooling systems, or produce large quantities of wastewater, which need to be treated. These industries include, but are not limited to, agriculture, petroleum, chemical, pharmaceutical, mining, metal plating, textile, brewing, food and beverage processing, and semiconductor industries. These industries are strictly regulated with regards to the level of contaminants in their discharge wastewater. Additionally, water drawn into the facilities for use such as in cooling towers, are drawn in from various supplies, such as river water, and contaminants and other compounds need to be removed so that they will not cause scale formations, nor in otherwise clog or damage the equipment used in the processes. Current techniques for treating such water include large settling ponds, clarifiers and filtration systems that include large amounts of polymer additives. Biological treatment of water for removal of dissolved organic materials is well known and widely practiced in many industries today. The process includes sedimentation of microorganisms in order to separate the microorganisms from the water and to reduce the amount of Total Suspended Solids (TSS) in the final effluent. The sedimentation step usually takes place in a clarifier unit. Thus, the biological process is constrained by the need to produce biomass that has good settling properties.
Membrane costs are directly related to the membrane area needed for a given volumetric flow through the membrane, or “flux”. Flux is expressed as liters/hour/m2 (LMH) or gallons/dat/ft2 (GFD). Typical flux rates vary from approximately 10 LMH to about 50 LMH. These relatively low flux rates are due largely to the fouling of the membranes and slow processing down.
The membrane, for instance a microfiltration membrane, interfaces with “mixed liquor” which is composed of water, dissolved solids such as proteins, polysaccharides, suspended solids such as colloidal and particulate material, aggregates of bacteria or “flocs”, free bacteria, protozoa and various dissolved metabolites and cell components. In operation, the colloidal and particulate solids and dissolved organics deposit on the surface of the membrane. Colloidal particles form a layer on the surface of the membrane, while small particles can plug the membrane pores, a fouling condition that may not be reversible. Pore plugging and the colloidal layer on the membrane, increase resistance and decrease flux, thereby reducing the effectiveness of the membrane and requiring frequent cleaning.
Additionally, during periods of high organic loading, for instance, in cases involving river or pond water, when there are periods of high run-off into the water source or increased levels of rain which would increase the amount of sediments and TSS in the water sources, it is difficult to maintain optimum conditions. In such situations, it is found that the filtration systems, particularly the microfiltration systems, need to be cleaned or replaced on an even more frequent basis.
It is know in the art to process wastewater to remove certain contaminants. For instance, U.S. Pat. No. 5,904,853 discloses a process for removing metal and certain non-metal contaminants by treating with a chemical coagulant. In U.S. Pat. No. 6,428,705, a process and apparatus for removing g metals and other inorganic and organic contaminants from large volumes of wastewater is taught, where in chemical coagulants of a specific nature and molecular weight are used. In U.S. Pat. No. 6,926,832 the use of water soluble cationic, amphoteric or zwitterionic polymers to condition mixed liquor in membrane biological reactors resulting in reduced fouling and increased water flux through the membrane is taught.
However, a need still exists for an efficient and effective process that would decrease the fouling of the microfiltration systems, providing less frequent cleaning and/or replacement and would enhance the overall filtration process.